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- Scherstén, Anders, et al.
(författare)
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Re-Os and U-Pb constraints on gold mineralisation events in the Meso- to Neoarchaean Storo greenstone belt, Storo, southern West Greenland
- 2012
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Ingår i: Precambrian Research. - : Elsevier BV. - 0301-9268. ; 200, s. 149-162
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Tidskriftsartikel (refereegranskat)abstract
- The Storo greenstone belt in Godthabsfjord, southern West Greenland consists of juxtaposed rock units of different age and origin, and hosts gold mineralisation that is associated with arsenopyrite along a contact between lithological units and along the axial plane of a large fold core. The age and origin of the gold is debatable, but in this paper, we present new arsenopyrite Re-Os and zircon U-Pb data to constrain the age of the Storo gold deposit. A 2.71 +/- 0.05 Ga arsenopyrite isochron and 2.707 +/- 0.008 Ga highly radiogenic arsenopyrite from a mineralisation along a rock contact, together with a 2.64 +/- 0.02 Ga arsenopyrite isochron along the axial plane of the fold core indicate a two-stage mineralisation process. While the 2.707 +/- 0.008 Ga highly radiogenic arsenopyrite provides firm support for an early mineralisation event, a mixing origin cannot yet be excluded for the 2.71 +/- 0.05 Ga isochron. The 2.64 +/- 0.02 Ga isochron is in perfect agreement with recent U-Pb zircon data (Nutman et al., 2007. Precambrian Research 159, 19-32) and these data are best explained by orogenic mineralisation during amphibolite facies metamorphism along structural weak planes. The initial Os-187/Os-188 value of 0.56 +/- 0.16 for the 2.64 +/- 0.02 Ga isochron indicates a crustal source for the metals, whereas the initial Os-187/Os-188 = -0.1 +/- 0.6 for the 2.71 +/- 0.05 Ga isochron remains unconstrained. Re-Os data are best explained by relatively short crustal residence times of less than 0.1 Ga, wherein the Os, and associated metals, were extracted from the mantle at a time younger than 2.8 Ga, and in which the 2.64 +/- 0.02 Ga stage formed by mobilisation of an earlier mineralisation. Detrital zircon constraints imply volcanism and sediment deposition for parts of the belt at <= 2.84 Ga and that these units were tectonically juxtaposed to similar to 3.05 Ga rocks within the belt. The units that were deposited <= 2.84 Ga record metamorphic zircon U-Pb ages of similar to 2.63 Ga, but evidence for 2.72 Ga metamorphism, which is ubiquitous in adjacent terranes, is lacking. (C) 2012 Elsevier B.V. All rights reserved.
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